The present invention relates to content protection, and more specifically, to media key blocks in broadcast encryption systems.
Broadcast encryption is an important cryptographic key management approach, especially useful in content protection systems. Two popular broadcast-encryption-based systems are the Content Protection for Recordable Media (CPRM) system from IBM, Intel, Panasonic, and Toshiba, and the Advanced Access Content System (AACS) from Disney, IBM, Intel, Microsoft, Panasonic, Sony, Toshiba, and Warner Bros.
A media key block is the fundamental structure in broadcast-encryption-based system. This structure is also sometimes called a session key block. A media key block is a data structure which is processed by a device using a set of device keys. The result of the processing allows the device to calculate a media key. The media key, in turn, is used to decrypt a message. In content protection systems, these “messages” are actually content like video or music. Often in a content protection system, each piece of content is associated with a different media key block.
In some cases, the media key block is associated with a set of devices, not a particular item of content. One such example is IBM's Advanced Secure Content Cluster Technology (ASCCT), in which all the content that devices can access is protected by a single media key block. This feature is useful, for example, in case where a consumer might have a library of entertainment content in his home, and wants that library to be freely viewed by all the devices he owns. It should be noted that in this single media key block, it is often the case that not all the content being protected is equally valuable. For example, the user might have some movies in standard definition and some movies in high definition. From the point of view of the movies' creators, the high definition version is more valuable, and would have more serious economic consequences if the users were to make unlimited unauthorized copies. Likewise, not all devices are equally privileged. There is no reason, for example, why a standard definition television needs a set of keys that allows it to decrypt high-definition video.